Needle valves are used in a variety of applications where dosing of fluid is required. A needle-shaped component is able to move within a valve body, with the needle tip adapted to rest on a seat at a nozzle tip of the valve body. Nozzle apertures are provided at the nozzle tip. The nozzle apertures are blocked when the needle tip rests on the seat. When the needle is forced away from the seat—for example, by hydraulic pressure within the valve—then fluid flow may take place. The needle will restrict flow unless the needle tip is moved some distance away from the seat, so this design of valve is suitable for precise dosing of fluid. A context in which such valves are regularly used is that of a fuel injector, such as the fuel injector of a common rail fuel injector system.
A needle valve for a fuel injector needs to meet a number of performance criteria: it needs to withstand a range of operating pressures, it needs sufficient structural strength and good resistance to wear to allow it to operate reliably over a good operating life, and it should be easy and cheap to manufacture and use. It is desirable to provide a needle valve that will perform better than conventional needle valves in respect of these performance criteria, particularly in respect of a fuel injector for use in a common rail fuel injector system for a diesel engine.
Developments on conventional needle valves are taught, for example, by US2009/0179166, DE 19503224 and WO 2004/106726. These all teach new designs of needle valves for use in gasoline injectors for specific technical purposes. US 2008/018101, published after the priority date of the present application, describes a number of multi-part needle designs for use in needle valves.